Method of making electrical cable



Nov. 3, 1953 J. J. MORRISON 4METHOD OF' MAKING ELECTRICAL CABLE original Filed Feb. 2e, 194e IO Conductors I7 Ground Conductors I3 Meallc Shield Il I6 Outer Ru bber Jacke? INVENTOR. JAMES J. MORRISON,

ATTORNEY Patented Nov. 3, 1953 METHOD OF MAKING ELECTRICAL CABLE James J. Morrison, Worcester, Mass., assigner to United States Steel Corporation, a corporation of New Jersey Original application February 26, 1946, Serial No. 650,348. Divided and this application January 25, 1949, Serial No. 72,574

1 Claim. l

This invention relates to improved electrical cables and methods by which they are made and is a division of my copending application, Serial No. 650,348, led February 26, 1946, now abandoned. The invention has particular reference to portable cables that are subjected to rough handling and are exposed to mechanical shock in service.

Such cables, particularly of the rubber or rubber-like jacketed type, are subjected to extremely rough handling in normal service in mining operations, excavation Work in general contracting, rock quarrying, dredging and the like. Shock from falling rock and construction materials, being run over by trucks and movable equipment, and other rough usage is common, and, unless suflicient protection is given by the jacket and fillers of the cable, the insulation on the individual electrical conductors may be damaged, with resulting failure of the cable.

It is common practice to use llers of iibrous material, such as jute or cotton, to round up the cable core when the conductors are cabled into the required multiple conductor form; preformed rubber Jpr rubber-like fillers may also be used for a like purpose. It is also common practice to fill the interstices between conductors with rubber or rubber-like compound by the extrusion process, the ller being bonded, if desired, with the later applied jacket by a nal vulcanizing process. Such llers, in addition to making the cable round, must also serve as a cushion base for the jacket for nal absorption of the shock from blows received in service. Fillers of the brous type, as well as those of rubber or rubber-like material, however, often lack sumcient elasticity for such desired cushioning action. The fibrous fillers tend to pack and become hard, as well as being subject to freezing in cold Weather from entrained moisture, While rubber or rubber-like llers are stiff and also increase the weight of the completed cable.

An object of this invention is to provide a cable construction and method of manufacture which will provide an increase in cushioning action by the iillers while retaining the advantages of rubber or rubber-like material in the elimination of water absorption in such iillers. Itis also an object of the invention to produce a reduction in Weight of the completed cable.

These results are accomplished by this invention by the use of sponge rubber or rubber-like material for such fillers, the fillers of such composition and structure in the completed cable providing a maximum of cushion elect for the absorption of shock and blows on the cable jacket with delinite protection to the insulated conductors forming the cable core.

In the accompanying drawings:

Figure l is an elevation of the cable made in accordance with a preferred embodiment of this invention, portions of the cable being broken away to reveal the interior structure of the cable; and

Figure 2 is a cross sectional view of the same cable, the section being taken along line Il--II of Figure 1.

Referring particularly to the accompanying drawings, the numeral I indicates conductors which preferably are composed of stranded copper wires. The conductors I!) are provided with a layer of insulation II and are positioned adjacent to each other. The insulation I I may be of rubber, rubber-like material, synthetic resin, varnished oambric, paper, fabric, or other suitable material as desired. Over the insulation II is provided a fibrous or fabric cover I 2 so that the conductors I@ are furnished with additional protection and means of identification as by color of cover I2 or other suitable means. A further protection for the conductors may consist of a metallic shielding I3, in the form of a braid, tape, or Wire Wound thereabout, to reduce static stresses and provide a safe and continuous ground connection.

The individually insulated conductors, so constructed, are laid up together, as in the three conductor form of cable shown in the drawings. If required for additional ground capacity, grounded conductors I'I may be pla-ced in the interstices formed by the cabled individually insulated conductors. Over the assembled conductors is placed a protective jacket composed of the inner jacket and filler I4 and a dense, tough, outer jacket I6,

- such outer jacket being composed of rubber or rubber-like material. Between the outer jacket I6 and the inner jacket I4 may be placed a reinforcing wind or braid of cotton cord I5. The inner jacket I4 is likewise composed of rubber or rubber-like material, but in such material there is included a substantial quantity of a blowing agent which will form gas during vulcanization, thus producing a sponge-like condition in the filler and inner jacket. The cable, after the application of the outer jacket IS, is then vulcanized, usually in a common type of mold or lead pipe, such operation vulcanizing both the inner jacket and filler I4 and the outer jacket I6, and bonding them together. With the construction described, the resultant jacket on the cable will be composed of an outer wear resistant section of a dense tough character and with an inner section and ller section of substantial thickness composed of spongy rubber or rubber-like material well adapted to absorb shock and external blows for the protection of the insulated conductor forming the core and, like- Wise, resulting in a lighter weight cable than with the use of regular dense inner jacket and fillers. By the use of a crepe type of tape covering over the assembled core-before application of the filler and jacket as outlined in United, States Patent- No. 2,286,827, the sponge effect will be increased due to the increased expansion volume available for the sponge condition of jacket andmiillerY I 4 to form in the interstitial spaces betweenthe conductors and with consequent improvement in-` called 60% tire stock, containing naturalrubber` and carbon black. It is also possible to use for such jacket andlller I4 any of the lso-called-,syn-

thetic, rubbers which are vulcanizable, such as` polymers ofchloroprene, sold under` the` trader names Neoprene, Sovprene, and GR-M, copoly` mers=of butadiene and styrene, sold; under the trade names Buna S, Chemigumv IV, Hycar OS, and GR--S, polymers of butadiene, soldunderthe tradenames Buna 85, Buna- 115, SKA, and SKB, copolymers of butadiene and acrylonitrile, sold underthe trade names` Perbunan, Buna N, Perbunan Extra, Chemigum III, Hycar OR, and Thiokol RD, and copolymers of iscbutylene and butadiene or isoprene, sold-under the trade names Butyl or GR-I. It is to be understood that the above list isnot exhaustive, and that various otherY vulcanizable elastomers, natural or synthetic, may beernployed.

The blowing agent to be employed is thoroughlyI dispersed throughout the material oil-which jacket and illler I4 is to be formed before itv is molded about the conductors.; Such agent may be sodium bicarbonate, ammonium carbonate, or other similar materials or mixtures of materials well-known assponging ory blowing agents in the rubber working art.

Anamount. of; blowing agent is usedl which. is sufficientto; ycause the material forming inner jacketl and; iller I4 to expand in volume in amounts; from 25- to 100% whenv such material is vulcanized in plaoein the cable. In one preferred embodiment suchamount of expansion of volume after Vulcanization is 40%.y Such expansion of the inner jacket and filler is a direct measure of4 the volume of the voids in thesponge inaterialf as` it occurs in the finished cable. volume of the voids. thus4 may range from 25; to- 100% of the volume of the elastomer per se in the sponge material, careI of by a flow of the` material I4 into the spaces between the insulated conductors I andbetween suchv conductors' and grounded, conductors` Il, ii; such are employed, andf by an expansion of the outer jacket I6, tosome extent, `clue to the outwardly directed pressure exerted by the expanded, vulcanized, inner jacket andller I4.

As a specific example of a composition suitable for use in the making of jacket and i'lller I4 thereA is given the following, which is illustrativeonly,Y all parts being given by weight:-

Parts (Erft-SV 100 Factice 200 Zn() 40 Litharge 8 Sulphur 2 Accelerator 2 Sodium bicarbonate 80 Stearic acid i0v Processing oi1 12V Such Suchl expansionv is taken The `above compositiorrV ismixed; in accordance with, conventional rubberA practice, asV for example, in a Banbury mixer, and is then applied in a conventional manner to the assembly of conductors andmgqroundedncables, as by the extrusion process. It 'willfbeA understood that various ingredients iny theaboye composition may be replaced byotherfknown equivalents. For instance, in place; of stearic acid any fatty acid may be employed,- The processing oil may be a mineral oil` suchasparaflin; oil or the wel1-known oil for such,` purpose marketed under the trade name Circo Oil. Factice, which is an ingredient of theabove composition, is a vulcanized vegetable oil customarily employed' as a softener and iiller for rubber andrubber-likematerials The outer jacket IIi o f the electrical cableemaw be made ofV naturalrubber, natural rubber with a filler such as.- carbon black, onany one'ofjthei vulcanizablevelastomers set outv as usefulin in ing the innerjacket and iiller I4, thechoicesuch; elastomer depending4 upon the panticular properties Adesired in the nished outer` jacket.A

The outerjacket may likewise beapplied tothe cable cover and` intimate contact with theinner; jacket and filler by-an extrusion process.

Inthe accompanying drawings, a construction indicating three conductorsis, shown, and the,

cable has a jacket as sole outerprotectiinbuti the 'featuresof the inventionwill apply te any-- cable of one'or moreconductors, and additional;

outer protective coverings may be appliedA ifa desired.

While I have shown; and described` a specific embodiment of this invention, .it must be under,-`

stoodthat Ido not` WishV to be limited exactly thereto sincevarious modifications may bem-ade,

without departing-from the scope` Ofthe.V invention as outlined bythe appended claim.

I claim:

In the manufacture of cables for the trans,"` mission of electric current, themeth od whichy comprises assembling a plurality of insulated conductors so as to have valleys between them, extrudingan inner jacket and ller of, a vulcanizable elastomer completely. around and into. contact with the assembled conductors, such elastomer' containingV a sufficient quantity'.V orf` a blowing agent to cause the elastomer to expand in .volume from 25 to 100% Whenvulcanized in,

place aroundthe cable, extrudingy an outer jacket forming body laround theinner jacketand filler, the outer jacketforming body being composed, Qi`

a vulcanizable elastomer ciV such composition thatwhen vulcanized it forms a den, tough: material, saidv outer jacket having an inner di,-

ameterr greater than the outer diameter o fr said assembled conductors,` and then subjecting the` cable to heat to cause the first named elastomer to expand inwardly into said valleys and out,- wardly against said outer jacket to expand-j the` same and to vulcanize the inner` jacket,v iiller and outer jacket and to` bond them directly together'f throughout' the inner periphery of the outerl jacket.y

JAMES J. MORRISON;

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,149,002 Wermine Feb, 28, 1939` 2,186,793 Wodtke Jan. 9, 1940 2,518,454 Elliott Aug. 15, 1950 

